NOTE Olson and Scholey Growth of late-larval and early-juvenile Euthynnus line^tus 



827 



(1956) and Harada et al. (1973, 1974, 1980) are within 

 the range of growth rates reported here, although we 

 obtained greater rates too, up to 4.8 mm/day. Clemens 

 (1956) stated that his results probably approximate 

 minimum growth rates in nature. 



An undesirable aspect of our study was the neces- 

 sity of estimating, rather than measuring, lengths at 

 the time of capture. This may have contributed to the 

 large variance in the data reported for the first 15 days 

 (Fig. 5b). Estimation errors were minimal, however, 

 because the second author's ability to estimate lengths 

 of live fish was continually refined by estimating, then 

 measuring the fish that died in the tanks soon after cap- 

 ture. Except for a few fish held for short times, max- 

 imum estimation errors of ± 4 mm translated to low 

 potential error in growth rates. 



Despite unavoidable estimation errors, this study 

 reveals some interesting aspects of growth of young 

 tunas. Black skipjack are capable of growing at high 

 but variable rates when food is plentiful. The growth 

 rates we measured might be considered upper limits 

 for this species; feeding to satiation in the wild would 

 likely be detrimental to survival because laboratory 

 observations suggest that the added weight of food in 

 the gut inhibits mobility. The variability in rates mea- 

 sured during the early part of the experiments may be 

 due in part to the stress of captivity. However, high, 

 variable growth rates suggest a large scope for gi'owth 

 (Brett 1979), an advantageous characteristic for fish 

 that spend their early life stages in the epipelagic zone 

 where predation risk is great. A large scope for growth 

 permits rapid gi'owth when food is abundant, providing 

 young tunas an earlier transition to piscivorous feeding 

 and early formation of schools. The decline in growth 

 rates with increasing time in captivity may be related 

 in part to inadequate-sized rearing containers (Thei- 

 lacker 1980). Further laboratory growth experiments 

 should concentrate on maintaining constant, controlled 

 rations. 



Growth rates of late juvenile and/or adult black skip- 

 jack from the commercial catch in the eastern Pacific 

 Ocean are much lower, as expected, than those re- 

 ported here. Tagging and length-frequency modal 

 progression analyses provided rates that agree with 

 each other (Peterson 1983:54-55). Black skipjack 

 measuring 32-45 cmFL grew about 0.36 mm/day. 

 Larger fish, 45-51 cm, gi-ew more slowly, 0.22 mm/day. 

 The upper seven data points in Figure 5a, correspond- 

 ing to the largest fish (224-272 mmSL) which were held 

 for the longest times (59.5-167.5 days), appear to 

 represent a slower growth stanza than a previous 

 stanza <60 days. A straight line fitted to these seven 

 points yielded a significant slope of 0.28 mm/day, com- 

 parable to the natural growth rates reported for 32- 

 to 51 -cm black skipjack (Peterson 1983:54-55). 



jack tuna Katsuwonus pelamis, another primitive 

 species of the tribe Thunnini, measuring 37.5-42.5 

 cmFL when tagged and released east of 100°W longi- 

 tude grew an average of 1.22 mm/day in 31-180 days 

 at liberty (Bayliff 1988b). 



Much additional work on growth of tunas under con- 

 trolled conditions, as well as growth studies in nature, 

 is needed to understand how physical and biotic vari- 

 ability in the ocean affects growth rates and life-stage 

 duration. By virtue of black skipjack's biological sim- 

 ilarities to commercially important tunas, we believe 

 that such studies utilizing black skipjack tuna will yield 

 important information that would be applicable to other 

 tunas. 



Acknowledgments 



We wish to thank the staff members of the Achotines 

 Laboratory for their hard work and long hours. R.R. 

 Lauth and R.C. Jope provided special assistance with 

 weight-length and laboratory temperature data. We 

 acknowledge the efforts of G. Schumann, B.M. Chat- 

 win, and J.M. lanelli for much of the early development 

 of the Achotines Laboratory. The Panamanian Minis- 

 terio de Comercio e Industria, Departamento de Recur- 

 sos Marinos, has provided continued support of the 

 Achotines Laboratory. Valuable reviews were provided 

 by W.H. Bayliff, W.L. Klawe, R.R. Lauth, D. Mar- 

 gulies, K.M. Schaefer, and two anonymous reviewers. 



Citations 



Bayliff, W.H. 



1988a (editor) Annual report of the Inter-American Tropical 

 Tuna Commission, 1987. Inter-Am. Trop. Tuna Comm., 222 p. 

 1988b Growtli of skipjack, Katsuworms pelamis, and yellowfin. 

 Thunnus albacares, tunas in the eastern Pacific Ocean, as 

 estimated from tagging data. Inter-Am. Trop. Tuna Comm. 

 Bull. 19:307-,385. 

 Brett. J.R. 



1979 Environmental factors and growth. /« Hoar, W.S., D.J. 

 Randall, and .J.R. Brett (eds.), Fish physiology. Vol. VIII. 

 Bioenergeties and growth, p. 599-67,5. Acad. Press, NY. 

 Calkins, T.P.. and W.L. Klawe 



1963 Synopsis of biological data on black skipjack, Euthynnus 

 llueatus Kishinouye 1920. FAO Fish. Rep. 6:130-146. 

 Clemens, H.B. 



1956 Rearing larval soombrid fishes in shipboard aquaria. 

 Calif. Fish Game 42:69-79. 

 Collette, B.B., and C.E. Nauen 



1983 F.-\<) species catalogue. Vol. 2. Scombrids of the world. 

 An annotated and illustrated catalogue of tunas, mackerels, 

 bonitos. and related species known to date. FAO Fish. SjTiop. 

 125. Vol. 2. 137 p. 

 Draper, N.R.. and H. Smith 



1981 Applied regression analysis. Wiley, NY. 709 p. 



